The invention relates to the formation of semiconductor devices. More specifically, the invention relates to the formation of semiconductor devices by etching features in an etch layer through a photoresist (PR) mask.
During semiconductor wafer processing, features of the semiconductor device are defined in the wafer using well-known patterning and etching processes. In these processes, a photoresist (PR) material is deposited on the wafer and then is exposed to light filtered by a reticle. The reticle may be a glass plate that is patterned with exemplary feature geometries that block light from propagating through the reticle.
After passing through the reticle, the light contacts the surface of the photoresist material. The light changes the chemical composition of the photoresist material such that a developer can remove a portion of the photoresist material. In the case of positive photoresist materials, the exposed regions are removed, and in the case of negative photoresist materials, the unexposed regions are removed. Thereafter, the wafer is etched to remove the underlying material from the areas that are no longer protected by the photoresist material, and thereby define the desired features in the wafer.
Argon-fluoride (ArF) excimer laser having wavelength of 193 nm has been used to produce most highly integrated circuits such as sub 0.04 μm devices. This technology, combined with immersion lithography (ArF lithography), enables processes below the 110 nm node. Such small circuit features require higher resolution and thus a thinner photoresist because of the depth-of-focus (depth-of-field) limitations of the patterning image. For example, the ArF lithography for certain DRAM processes, such as Bitline, uses a very thin photoresist with a thickness less than 100 nm. The photoresist material is also softer and weaker, and such a thin and weak photoresist mask would easily and undesirably be etched or damaged during a plasma process after the patterned photoresist mask is provided.